This invention relates to the field of solid state electronics and particularly to lateral bipolar transistors fabricated from III-V compounds.
Lateral bipolar transistors are potentially key elements in many integrated circuits, particularly digital circuits. Compared with vertical bipolar transistors or with conventional heterojunction bipolar transistors (HBTs), they offer a number of advantages such as:
(1) Their fabrication is potentially simpler because all key layers are at or near the surface, rather than being buried as in a conventional HBT;
(2) They operate naturally in the low current regime of interest for large scale integrated circuits (LSI) (by contrast, it is hard to efficiently operate vertical HBTs at low current because the emitter area must be kept large due to photolithographic limitations);
(3) Their base resistance can be low because of the proximity of the base to the surface; and
(4) They can be easily integrated with other circuit elements such as Schottky diodes, metal semiconductor field effect transistors (MESFETs), saturated resistors, etc.
In comparison with MESFETs or high electron mobility transistors (HEMTs), the lateral bipolar transistors offer advantages such as:
(1) higher transconductance;
(2) higher current handling capability; and
(3) potentially more uniform turn-on voltage.
Until the present invention, a major problem with lateral bipolar transistors is their difficulty of fabrication. For adequate current gain and cutoff frequency, the base width should be small, generally in the submicron regime, a size which is hard to obtain using conventional methods.